As is known in the art, efficiency improvement of radio frequency (RF) systems which employ one or more power amplifiers (PAs) can be achieved through supply (e.g. drain or collector) modulation, in which a voltage applied to the one or more PAs is dynamically changed according to characteristics of an RF signal being generated. A drain voltage can be changed on a time scale that is slow compared to amplitude variations of the RF signal (e.g., “adaptive bias”), or can be changed on a time scale in accordance with rapid variations of the RF signal amplitude (e.g., as is done in envelope tracking, polar modulation, “class G” power amplification, multilevel backoff, multilevel linear amplification with nonlinear components (LINC), Asymmetric Multilevel Outphasing (AMO), etc.).
Some systems providing drain modulation dynamically select an intermediate voltage from a set of discrete voltage levels, and then provide further regulation to synthesize a continuously variable drain voltage (e.g., for partially realizing a desired envelope in the output, e.g., “envelope tracking”). Other systems directly switch the drain voltage among discrete voltage levels. Such systems include “class G” amplifiers, multi-level LINC (MLINC) power amplifiers, asymmetric multilevel outphasing (AMO) power amplifiers, and multilevel backoff amplifiers (including “asymmetric multilevel backoff” amplifiers) and digitized polar transmitters.
In each of the systems above, two important functions are: 1) providing means to create multiple supply levels from a single supply input, possibly including regulation of the multiple discrete supply voltages; and 2) providing means to rapidly and efficiently switch among the discrete supply voltages. These two tasks can be performed separately, or—in some cases—together. The first task is sometimes accomplished using a multi-output power converter to synthesize multiple supply levels from a single input, and then using a switching network to select from among them. Multiple levels can be realized using a variety of techniques such as through multi-output magnetic converters, and/or through the multi-output switched-capacitor converters, and use of a plurality of converters. The second function is sometimes provided by selecting from among the set of discrete voltage levels via a switching network. These two functions can be performed together in a single structure, such as through use of a reconfigurable switched-capacitor voltage modulator.